Chemistry of inorganic compounds – Carbon or compound thereof – Binary compound
Reexamination Certificate
1999-08-10
2002-07-09
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Binary compound
Reexamination Certificate
active
06416728
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for producing iron carbide (Fe
3
C) suitable for raw materials for iron making or steel making which comprises iron carbide (Fe
3
C) as a main component, for example, raw materials for steel making which is used in an electric furnace and the like.
BACKGROUND ART
The production of steel normally comprises the steps of converting iron ore into pig iron using a blast furnace, and then converting the pig iron into steel using an open hearth furnace or a converter. Such a traditional method requires large amounts of energy and large-scale equipment, and has a high cost. Therefore, for a small-scale steel making, a method comprising the steps of directly converting iron ore into raw materials to be used in a steel making furnace, and converting the raw materials into steel using an electric furnace and the like has been used. With respect to this direct steel making process, a direct reduction process has been used to convert iron ore into reduced iron. However, the reduced iron produced by the direct reduction process is highly reactive and reacts with oxygen in the air to generate heat. Therefore, it is necessary to seal the reduced iron with an inert gas or by some other measures during transportation and storage of the reduced iron. Accordingly, iron carbide (Fe
3
C) containing a comparatively high iron (Fe) content, and which has a low reaction activity and can be easily transported and stored, has recently been used as the raw materials for steel making in an electric furnace and the like.
Furthermore, raw materials for iron making or steel making containing iron carbide as a main component is not only easy to be transported and stored, but also has the advantage that carbon element combined with iron element can be used as a source of fuel in an iron making or steel making furnace, and can be used as a source to generate microbubbles which accelerates a reaction in the steel making furnace. Therefore, raw materials for iron making or steel making containing iron carbide as a main component has recently attracted special interest.
According to a conventional method for producing iron carbide, iron ore fines are fed into a fluidized bed reactor or the like, and are caused to react with a gas mixture comprising a reducing gas (e.g., hydrogen gas) and a carburizing gas (e.g., a methane gas and the like) at a predetermined temperature. Thus, iron oxides (hematite (Fe
2
O
3
), magnetite (Fe
3
O
4
), wustite (FeO)) contained in iron ore are reduced and carburized in a single process (which means a process performed by simultaneously introducing a reducing gas and a carburizing gas into a single reactor) as shown in the following reaction formula ((1), (2), (3), (4)).
3Fe
2
O
3
+H
2
→2Fe
3
O
4
+H
2
O (1)
Fe
3
O
4
+H
2
→3FeO+H
2
O (2)
FeO+H
2
→Fe+H
2
O (3)
3Fe+CH
4
→Fe
3
C+2H
2
(4)
Furthermore, the formula (1) to (3) may be put together. As a result, the reaction formula for deciding the progress of reduction and carburization of iron oxide can be shown by the following reaction formula (5) and the above-mentioned reaction formula (4).
Fe
2
O
3
+3H
2
→2Fe+3H
2
O (5)
The prior art related to the field of the present invention has been described in the publication No. 6-501983 of Japanese Translation of International Patent Application (PCT/US91/05198), for example.
However, free carbon is sometimes generated depending on the producing conditions such as a gas composition, a reaction temperature and the like in a fluidized bed reactor. In a case where the free carbon is mixed with iron carbide, there come out the following drawbacks.
(1) There is a possibility that a dust fire or explosion might be caused by free carbon scattered in a gas exhausted from the fluidized bed reactor.
(2) An opening such as an inlet port for raw materials, an outlet port for product of the fluidized bed reactor is sometimes blocked by the free carbon.
(3) CH
4
is consumed with the generation of the free carbon. For this reason, CH
4
which is necessary for the generation of iron carbide is additionally required.
(4) Once the free carbon is generated, the generation of the free carbon is promoted.
In consideration of the above-mentioned problems of the prior art, it is an object of the present invention to provide a method for producing iron carbide in which free carbon is generated with difficulty.
DISCLOSURE OF THE INVENTION
In order to accomplish the above-mentioned object, the present invention can detect free carbon in a latter half of compartments in a reactor and change a composition of a reaction gas corresponding to a quantity of the detected free carbon, thereby controlling the generation of the free carbon.
More specifically, the present invention provides a method for preventing free carbon from being generated by thermal decomposition from carbon monoxide or hydrocarbon when raw materials for iron making or steel making mainly comprising iron carbide as a main component is produced by reducing and carburizing iron-containing raw materials for iron making mainly comprising iron oxides and iron hydroxides as main components using a reaction gas mainly containing hydrogen and methane, comprising the steps of dividing an inside of a reactor into a plurality of compartments, detecting the free carbon in a latter half of the compartments which are closer to an outlet port for product, and changing a composition of the reaction gas corresponding to a quantity of the detected free carbon.
As a process of detecting free carbon, it is possible to employ “a process of detecting free carbon based on a change of a temperature of a thermometer installed in the latter half of the compartments”, “a process of detecting free carbon by analyzing dust picked up by a dust pick-up device installed on an upper portion in the latter half of the compartments” or “a process of detecting free carbon based on a result of detection of a ratio of methane to hydrogen in gas picked up by a gas pick-up device installed on an upper portion in the latter half of the compartments”. In addition, these two or more processes can be combined.
As a process of changing the composition of the reaction gas in the reactor, it is possible to employ “a process of increasing steam in the reaction gas corresponding to the quantity of the detected free carbon”, “a process of increasing carbon dioxide in the reaction gas corresponding to the quantity of the detected free carbon” or “a process of decreasing the carbon monoxide or the hydrocarbon in the reaction gas corresponding to the quantity of the detected free carbon”. In addition, these two or more processes can be combined.
The above-mentioned change of the composition of the reaction gas can be performed by controlling the composition of the reaction gas to be introduced into the reactor.
The status of the change of iron-containing raw materials in the reactor according to the present invention having the above-mentioned constitution will generally be described. A part of raw materials in the compartments on the side closer to the inlet port for raw materials is converted into Fe by mainly reducing reaction. Then, the residual reducing reaction and the carburizing reaction into iron carbide (Fe
3
C) of the iron-containing raw materials are performed in the compartments on the side closer to the outlet port for product. If the carburizing reaction in which an upper limit of a ratio of conversion into Fe
3
C obtained at a certain H
2
O partial pressure is exceeded is carried out, free carbon is generated. By the following process, the free carbon is detected. Then, the composition of the reaction gas is changed by the following process corresponding to the quantity of the detected free carbon. Consequently, the generation of the free carbon can be controlled.
(1) Detection of Free Carbon
a. Change of Reaction Temperature
The change of a reaction temperature can be used as means for indirectly dete
Inoue Eiji
Miyashita Torakatsu
Nakatani Junya
Nakazawa Teruyuki
Nio Akio
Griffin Steven P.
Kawasaki Jukogyo Kabushiki Kaisha
Nave Eileen E.
Oppenheimer Wolff & Donnelly LLP
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